(1. 陕西科技大学 机电工程学院，西安 710021；
2. 西北工业大学 航空学院，西安 710072)
摘 要: 镁锂(Mg-Li)合金是现今最轻的金属结构材料，在航空航天及交通运输等领域具有重大的应用价值。但铸造镁锂合金绝对强度低限制了其发展和应用。在Mg-Li二元合金中添加铝(Al)、锌(Zn)和稀土元素钇(Y)三种强化元素制备Mg-Li-Al-Zn-Y五元铸态镁锂合金来提高镁锂合金的力学性能。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和力学性能测试对比研究添加稀土Y前后铸态Mg-8Li-3Al-3Zn合金中相组成、微观组织和力学性能，揭示稀土元素Y对铸态Mg-8Li-3Al-3Zn合金的增强机制和断裂机理。结果表明：铸态Mg-8Li-3Al-3Zn合金主要包含3种相：基体α-Mg、第二相AlLi和MgLi2Zn。添加1.0%(质量分数)Y后，铸态镁锂合金中AlLi相消失，并析出了大量富集在α-Mg晶界处的硬质Al2Y相，合金的晶粒发生细化。与Mg-8Li-3Al-3Zn(抗拉强度134.40 MPa、屈服强度96.46 MPa和伸长率7.5%)相比，Mg-8Li-3Al-3Zn-1Y抗拉强度、屈服强度和伸长率依次为189.99 MPa、128.2 MPa和7.8%，分别提高了41.4%、32.9%和4%。合金的断裂方式由解理断裂转变为准解理断裂。铸态镁锂合金力学性能的提高主要归因于Al2Y的形成及其对α-Mg相的细化作用。
关键字: 镁锂合金；稀土钇；显微组织；力学性能；增强机制
（1. College of Mechanical and Electrical Engineering, Shaanxi University of Science and Technology, Xi’an 710021, China;
2. School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China）
Abstract:The magnesium-lithium alloy is the lightest metal structural material and has great application value in the fields of aerospace and transportation at present. However, the development and application of as-cast magnesium-lithium alloy are greatly limited because of the low absolute strength. Three strengthening elements of aluminum (Al), zinc (Zn) and rare-earth element yttrium (Y) were added to obtain the as-cast Mg-Li-Al-Zn-Y alloy. The purpose is to use alloying to enhance the mechanical properties of Mg-Li alloy. The phase composition, microstructure and mechanical properties of as-cast Mg-8Li-3Al-3Zn-xY (x=0, 1) alloy were compared and analyzed by X-ray diffractometer (XRD), scanning electron microscope (SEM) and mechanical properties testing to reveal the reinforcement and fracture mechanism of rare-earth element Y on as-cast Mg-8Li-3Al-3Zn alloy. The results show that the microstructure of the as-cast Mg-8Li-3Al-3Zn alloy mainly consists of matrix α-Mg, AlLi and MgLi2Zn phases. With adding 1% Y (mass fraction), the AlLi phase disappears and a large amount of high-temperature hard phase Al2Y enrich at the primary α-Mg grain boundary. Moreover, the microstructure is significantly refined. Comparing with Mg-8Li-3Al-3Zn alloy (134.40 MPa, 96.46 MPa and 7.5%), the Mg-8Li-3Al-3Zn-1Y exhibits an optimum combination of tensile properties with the tensile strength, yield strength and elongation of 189.99 MPa, 128.2 MPa and 7.8%, which are improved by about 41.4%, 32.9% and 4%, respectively. The improvement of the mechanical properties is attributed to the secondary phase and grain refinement strengthening. By analyzing the fracture morphology, the fracture mode of as-cast alloy is changed from cleavage fracture to quasi-cleavage fracture.
Key words: Mg-Li alloys; yttrium; microstructure; mechanical properties; enhancement mechanism
